A refrigerator comprises a refrigeration system arranged to cool at least one compartment of the refrigerator. The temperature inside the compartment may be either above 0 degrees Celsius or below 0 degrees Celsius. A refrigerant circulates at least intermittently in the refrigeration system. The refrigeration system comprises a compressor, a condenser, an expansion arrangement, and an evaporator. Gaseous refrigerant is compressed in the compressor and condenses to liquid phase in the condenser. Passing through the expansion arrangement, the pressure of the liquid refrigerant is reduced. The liquid refrigerant at low pressure evaporates in the evaporator. The evaporator is arranged in thermal communication with the compartment of the refrigerator. Thus, the evaporator cools the compartment.
EP 1035387 discloses a refrigeration system comprising one compressor and an efficiency raising heat exchanger, referred to as a sub-cooler, arranged after the condenser before the expansion valve/arrangement. When a compressor of the refrigeration system is running, the so called sub-cooler is continuously flowed through by liquid refrigerant from an outlet side of a condenser and by gaseous refrigerant from an outlet side of an evaporator of the refrigeration system.
KR 2011-0116334 discloses a refrigerator and freezer with sub-cooler. From FIG. 3 of KR 2011-0116334 it may be deduced that the refrigerator/freezer comprises two parallel refrigeration circuits leading from a condenser via sub-coolers back to a compressor. It is apparent from FIGS. 3 and 4 of KR 2011-0116334 that refrigerant flows simultaneous thorough both parallel circuits and that the pressure is reduced to the same low level in both circuits before the gaseous refrigerant is introduced in the compressor. Apparently, the primary purpose of the refrigerator/freezer is to provide an efficient evaporation of refrigerant in the evaporator. Expansion losses in the refrigeration system illustrated in FIG. 3 of KR 2011-0116334 are the same as in the refrigeration system disclosed in FIGS. 1 and 2 of KR 2011-0116334, i.e. a refrigeration system without sub-coolers.
EP 658730 discloses a refrigeration system comprising a low stage compressor and two high stage compressors, and utilizing an economizer/sub-cooler. The refrigeration system may be utilized in air-conditioning and/or food coolers in a supermarket as well as frozen food cases in grocery stores. Valves are provided for selectively supplying gas from the economizer/sub-cooler to motors of the compressors or to the high stage compressor. In the refrigeration system high stage compressor capacity may be increased.
There exists a need for increased efficiency in single compressor refrigerators.